The present invention relates to shock absorbers that generate a damping force by controlling the flow of a hydraulic fluid in relation to the stroke of a piston rod.
Cylinder type hydraulic shock absorbers attached to suspension systems of vehicles, for example, automobiles, are generally arranged as follows. A piston connected with a piston rod is inserted in a cylinder having a hydraulic oil therein as a hydraulic fluid. A stroke of the piston rod causes sliding movement of the piston in the cylinder, which in turn induces a flow of hydraulic oil. The hydraulic oil flow is controlled by a damping force generating mechanism, which comprises an orifice, a disk valve, etc., to generate a damping force. In some shock absorbers of this type, a reservoir having the hydraulic oil and a gas sealed therein is connected to the cylinder to compensate for a cubic capacity change in the cylinder caused by the entry and exiting of the piston rod into and from the cylinder and a volumetric change of hydraulic oil due to a temperature change. That is, such a cubic capacity change and a volumetric change are compensated for by the compression and expansion of the gas in the reservoir.
In a shock absorber having a reservoir as stated above, if the gas in the reservoir gets mixed into the hydraulic oil as bubbles or dissolves in the hydraulic oil, aeration or cavitation may occur, causing the damping force to become unstable. Under these circumstances, Japanese Patent Application Publication No. Hei 9-264364 discloses a shock absorber having a baffle plate disposed above an opening of a flow path of hydraulic oil in the reservoir. With this structure, the baffle plate isolates the opening of the hydraulic oil flow path from the oil surface in the reservoir and allows the flow path area of hydraulic oil flowing into the reservoir to be enlarged gradually. Accordingly, it is possible to suppress the gas in the reservoir from getting mixed into the hydraulic oil as bubbles or from dissolving in the hydraulic oil and hence possible to suppress the occurrence of cavitation and aeration.